In light of the increasing awareness for environmental protection and workplace safety, a current major thrust of the adhesives industry is to develop an adhesive composition which avoids the use of highly volatile organic solvents which can cause damage to the environment and potentially affect the health of workers exposed to the solvent. It has thus far been relatively difficult to develop an aqueous adhesive which performs at a level equal to traditional solvent-based adhesives. One major problem associated with bonds formed from aqueous adhesives is the relative susceptibility of the bonds to high temperature fluids and corrosive materials. In applications involving the bonding of elastomeric substrates to surfaces such as metal surfaces, an aqueous adhesive must exhibit an affinity for the elastomeric substrate as well as possess the ability to withstand degradation by high temperature fluids or corrosive materials.
Various aqueous adhesives for bonding elastomeric materials have been developed in a continuing effort to obtain the ultimate aqueous adhesive for bonding elastomeric substrates. For example, U.S. Pat. No. 4,167,500 describes an aqueous adhesive composition that contains a water dispersible novolak phenolic resin, a methylene donor such as an acetal homopolymer or acetal copolymer, and water. The phenolic resins described are primarily derived from resorcinol and alkylphenols such as p-nonylphenol although various other polyhydroxy phenols are mentioned, such as phloroglucinol and pyrogallol.
U.S. Pat. No. 4,483,962 describes a terpolymer latex of an emulsion polymerized terpolymer of at least one 2,3-dihalo-1,3-butadiene monomer, at least one monoalkenyl aromatic alkylhalide monomer, and at least one olefinically unsaturated monomer. The terpolymer latex utilizes a surfactant such as an anionic surfactant or a mixture of an anionic surfactant and a non-anionic surfactant.
U.S. Pat. No. 4,988,753 describes an aqueous bonding composition containing (1) a mixture of chlorosulfonated polyethylene and vinyl chloride/vinylidene chloride/acrylic acid copolymer, (2) an organic polynitroso compound, and (3) a coreactive compound selected from diallyl acrylamide and phenylene bis-maleic acid imide. The adhesive composition may also optionally contain adhesion promoters, fillers, and processing aids.
U.S. Pat. No. 5,036,122 describes an aqueous adhesive composition which is a blend of a latex of a polymerized conjugated diene, a poly-C-nitroso compound, and a polymaleimide compound which is a polymer of a bismaleimide.
U.S. Pat. No. 5,496,884 relates to an aqueous adhesive composition comprising a polyvinyl alcohol-stabilized butadiene polymer latex and a methylene donor compound wherein the butadiene polymer latex is prepared by an emulsion polymerization in the presence of polyvinyl alcohol. The methylene donor comprises any compound which is compatible with the other ingredients of the adhesive composition and which is capable of forming a methylene bridge or linkage between the free hydroxyl groups of the polyvinyl alcohol-stabilized butadiene latex at elevated temperatures. U.S. Pat. No. 5,496,884 is hereby incorporated by reference.
Many of the previously developed aqueous adhesive compositions such as those described above do not provide adhesive performance at the same level as traditional solvent-based adhesive compositions. A need currently exists for an aqueous adhesive composition that will exhibit substantial affinity for an elastomeric substrate as well as produce a bond that will withstand harsh environmental conditions such as those caused by high temperature fluids and corrosive materials.